Process for cladding steel

ABSTRACT

A process for cladding of steels and the resulting product. A consistent and acceptable bond is obtained by providing a containment coating to prevent diffusion of the ingredients of the sub-strate into the cladding material. A desirable containment coating is one in which one of the constituents is provided by the sub-strate to provide a composite which is more stable than similar compounds of the cladding coat such as tantalum or columbium. This permits a chemical vapor deposition of the cladding without adverse reaction with surface ingredients. A further step in the process is available in the localizing of flow of gas in the deposition to bring them together just prior to contact with the shape to be coated.

United States Patent [191 Glaski Related US. Application Data [63] Continuation-impart of Ser. No. 117,929, Sept. 7,

[52] US. Cl. 117/71 M, 117/50, 117/93.] PF, 1 17/1052, 1 17/1072 [51] Int. Cl. C23c ll/00 [58] Field of Search; 1 17/1072, 107,106 R, 1l7/105.2, 93.] PF, 71 M, 50,148/635 [56] References Cited UNITED STATES PATENTS 12/1968 Heil ll7/71 M 4/l97l Wakefield..... ll7/107.2 4/1966 Rogers ll7/l07.2

3,ll5,957 3,574,66l 3,248,612

ooooooo Jan. 8, 1974 3,355,265 ll/l967 Hudson et al ll7/l07.2

Primary Examiner-Ralph S. Kendall Assistant Examiner l, \y MlsS i Attorney-Arthur Raisch et al.

[57] ABSTRACT A process for cladding of steels and the resulting product. A consistent and acceptable bond is obtained by providing a containment coating to prevent diffusion of the ingredients of the sub-strate into the cladding material. A desirable containment coating is one in which one of the constituents is provided by the sub strate to provide a composite which is more stable than similar compounds of the cladding coat such as tantalum or columbium. This permits a chemical vapor deposition of the cladding without adverse reac tion with surface ingredients. A further step in the process is available in the localizing of flow of gas in the deposition to bring them together just prior to contact with the shape to be coated.

3 Claims, 1 Drawing Figure PATENTEB JAN 8 I974 DOOOOOOO I 'A'MPYA OOOOOOO 1 PROCESS FOR CLADDING STEEL This application is a continuation-in-part of my copending application entitled Process for Cladding Steel." Ser. No. 177,929, filed on Sept. 7, 1971.

This invention relates to a process for cladding steels with tantalum or columbium and to the resulting prod- UCI.

There are certain applications of steel in which the product would be much enhanced by a cladding of tantalum on the surface to increase resistance to corrosion. The problem is to find an acceptable and reproducible bond between the tantalum and the steel and, secondly, to achieve uniformity over all the surfaces of a complex shape or a batch of complex-shaped hardware.

An attempt to deposit tantalum directly on steel containing carbon results in a poor bonding inasmuch as the tantalum combines with the carbon of the steel at an excessive rate leaving Kirkendall type porosity in the steel. It is possible to provide an excellent bond between tantalum and pure metals, such as molybdenum, chromium and iron; but as the carbon content of the steel increases, the bond becomes less satisfactory. In steels such as the stainless variety the carbon content may be reduced to the point of not causing objectionable combining with tantalum, but the high nickel content creates the problem here. In a CVD process, the nickel will diffuse rapidly into tantalum leaving again the objectionable porosity. I

The present invention contemplates a coating on steel which will protect the surface against the deterioration when tantalum is deposited by chemical vapor deposition. It is, therefore, an object of the invention to provide a process for cladding steel with tantalum or possibly columbium which is consistentlysuccessful and uniform.

It is a further object to provide a product of a tantalum clad steel resulting from the process and to provide a process which insures uniform results on complicated shapes.

Other objects and features of the invention relating to details of the process and the product will be apparent in the following description and claims in which the principles of the invention are set forth in connection with the best mode presently contemplated for the practice of the invention.

A drawing accompanies the disclosure and a single FIGURE thereof may be described as a diagrammatic illustration of an apparatus for accomplishing the present invention. I A

In connection with the problem of tantalum cladding of carbon containing steel, I propose to establish a containment surface on the steel which will prevent carbon diffusion from the steel substrate to the tantalum being deposited thereon.

By way of definition, an overcoat on a particular sub-strate is defined as the deposition of a measurable thickness of material on a surface. All electroplated coatings are overcoats; and, similarly, hydrogenreduced refractory metal halides in a chemical vapor deposition process results in an overcoat. In these depositions, all the components of the coating are provided by the plating bath or the plating gas and none are provided by the substrate.

I propose a containment surface on a substrate which might be defined as a displacement diffusion coating in which at least one of the constituents of the coating is provided by the sub-strate. In this process, the coating does not build up on the surface to any appreciable extent but rather grows into the: surfce. For example,

when titanium is used, this may be referred to as a ftitanizing process." The -izing" or -ized" suffix placed on the end of the name of the element deposited from the gas denotes such a reaction.

In connection with titanizing, there is a reaction of the titanium with the carbon in an atmosphere of TiCl, in the temperature range of 900-l ,100 C. which forms a thin diffusion barrier of titanium carbide. The TiCl, reacts with the surface carbon on the carbon steel sub-strate to form TiC and once' all surface carbon is reacted, the titanium deposition ceases. Thus, there is a definite limitation on the thickness of the displacement diffusion coating. Since titanium carbide is thermodynamically more. stable than TaC, the pure tantalum may be deposited without further carbon diffusion from the substrate. In the preparation of the displacement diffusion coating, there may be a reaction with free carbon on the surfacewith the TiCl but, in genera], the carbon is available primarily from metal carbides in the sub-strate which are less stable than TiC. Nearly all the metal carbides normally occurring in carbon steel and low alloy carbon steel are less stable than TaC and thus displacement diffusion coating is required. t

While titanium has been mentioned above, it is possible to use a containment coating of a metal selected from Groups Nb and Vlb, iron, and cobalt. Of this group, for example, titanium carbide and ZrC are both more stable than tantalum carbide. After this containment coating is applied, it is possible to overcoat with pure tantalum in a CVD process without further carbon diffusion from the sub-strate.

In connection with stainless steels which are high in chromium and nickel, the problem with carbon diffusion is reduced since the carbide with chromium, namely, Cr C is very stable. On the other hand, the nickel content of the stainless steel will diffuse uncontrollably into a tantalum clad coat. Thus, for these steels, an overcoat of the pure metal to which tantalum may be bonded in a CVD process must be used. In some instances, a plating process may be used and in other instances a plasma spray can provide acoating to which tantalum may successfully bond. In each case, care must be used to obtain a good bond between the sub-strate and the overcoat. With electroplating, careful pre-plating procedures must be observed in the cleaning of the part and well controlled plating steps must be utilized. In the plasma spraying, a coating of pure iron, chromium, cobalt, molybdenum of tungsten may be applied; in fact, any of the metals from Group lVb and Group Vlb as well as iron or cobalt can be practically applied in this way.

Once the pure metal overcoat is applied to the stainless steel, the nickel diffusion is blocked and the CVD coating or clad of tantallum can be readily applied using conventional procedures.

It will be appreciated that carbon steel can also be plated or plasma sprayed with pure metals as above described to block carbon diffusion. With steel castings, for example, they are sometimes ground out and plasma coated with iron to remove the surface porosity and then titanized to stabilize any'carbon that may have diffused into the plasma coat. Then the tantalum clad may proceed with a resulting good quality and uniform coat.

With respect to the use of plasma spray of iron on stainless steel, the carbon diffusion is not as critical a problem since the iron interlayer remains pore iron and the bonding of the CVD tantalum readily occurs without titanizing.

It has also been noted in tantalum cladding that deposition has occurred preferentially on certain areas of exposed parts rather than uniformly or in the areas where it is most generally desired. Tantalum cladding has been much improved by a control of the mixing of the tantalum C1 and the hydrogen reactant gases.

In the chemical vapor deposition process which otherwise proceeds in accordance with accepted procedures in a reduction reaction, better results have been obtained when the TaCl is introduced to the chamber 7 in the normal manner as indicated in the drawing. However, the hydrogen is introduced through a separate feed line ora plurality of feed lines which terminate immediately upstream of the object to be coated. in other words, the gases are intentionally separated until they impinge on the object to be coated. This provides excellent control in putting the tantalum deposit where it is desired. Utilizing this technique, uniform tantalum claddings have been obtained on batches of cast valve bodies, for example, during a 45-minute deposition period in a system that formerly could not generate tantalum coverage over all areas of the valve bodies during a 5-hour period of deposition. Thus, there is a great savings in materials and expense in performing the process as well as a much more desirable and uniform re sult. ln some instances, a control of this combined flow which is brought together immediately upstream of the area to be plated can be improved by using multiple exhaust ports which are balanced to direct the flow to certain areas of the parts to be exposed.

While the above description has referred to tantalum cladding, it will be appreciated that columbium (niobium) is chemically similar and may be applied as a cladding coat in the same way as has been described in connection with tantalum. The same problems which require a containment coat for tantalum exist in relation to columbium. There is a considerable savings in the use of columbium since it is a less expensive metal but, on the other hand, tantalum has a broader applicability as a corrosion resistant material.

Following are three examples of a process used for steel cladding with sub-strates of differing carbon and stainless steels and various treatments prior to the titanizing and the application of the tantalum clad.

EXAMPLE 1-CLADDING OF 6 INCHES I.D.

X 24 INCHES LONG PIPE SPOOL MADE OF TYPE A-l06 CARBON STEEL l. Sand blast surface to remove scale and roughen surface for subsequent plasma sprayed coating.

2. Plasma spray 0.002 inch thick coating of iron on ID. and flange seal faces.

3. Place in CVP (chemical vapor deposition) furnace, evacuate with vacuum pump and heat to titanizing temperure of 1,070 C. in argon.

4. Bubble hydrogen at 2 liters/minute through liquid TiCl, and mix with the resultant gas 7 liters/minute of pure hydrogen (STP) and flow the mixture through spool, over flange seal faces and ID. surface for 1/2 hour at l,070 C. and 23 inches Hg. pressure.

5. After titanizing, adjust temperature to 1,0l0- 1,040 C. range and begin tantalum deposition by flowing 3 liters/minute of chlorine through heated tantalum chips to form TaCl and mixing the resultant gas with l8 liters/minute of hydrogen, passing it through the spool at 34 torr pressure. All gas flows at STP.

6. After l/2 hour, adjust gas flows to 7.5 liters/minutes of chlorine and 45 liters/minute of hydrogen, both at STP. v

7. Total tantalum deposition time 6% hours.

8. Turn off chlorine and hydrogen and cool in argon.

9. Resultant deposit thickness from 0.009 inch to 0.015 inch over both flange seal faces and ID. of spool.

EXAMPLE 2-CLADDING OF TYPE 316SS PUMP HOUSING WITH 1 INCH FORTS AN E FLA N GES AND 4% INCH DIAMETER CAVITY l Degre aseari d descale EH01 base commercial descaler solution.

2. Place in CVD furnace, evacuate with vacuum pump and heat to titanizing temperature at 1,000 C. in argon.

3. Bubble hydrogen at 2 liters/minute (STP) through liquid TiCl and mix the resultant gas with 7 liters/minute of pure hydrogen and flow the mixture through pump housing; over flange seal faces and inside surface for 1 hour at l,00O C. and 23 inch Hg. pressure.

4. After titanizing, adjust temperature to l,0l0 1,030 C. range and begin tantalum deposition by flowing 1.5 liters/minute of chlorine through heated tantalum chips to form TaCl and mixing with 9 liters/minute of hydrogen, passing the mixture through the pump housing at 30 torr pressure. All gas flows at STP.

5. Total tantalum deposition time 5 /2 hours.

6. Turn off chlorine and hydrogen and cool in argon.

7. Resultant deposit thickness from 0.012 inch to 0.020 inch over both flange faces and inside surface of pump housing.

THIERMtTWELL, 374 INCH" DIAMETER 50'1"" LONG WELL wITH 2 /2 INCH DIAMETER (FLAT-TO-FLAT) X 2 INCH LONG HEXAGONAL BASE. TOTAL LENGTH 6 INCHES lflje grease and (Iescale in'HCl base commercial descaler solution.

2. Place in CVD chamber, evacuate with vacuum pump to heat directly by induction to titanizing temperature at l,l00 l.l25 C. after baking in H at l,050 l,075 C. for 10 minutes.

3. Bubble H at 800 cc/minute through liquid TiCl and mix the resultant gas with 3.5 liters/minute of pure hydrogen (STP) and flow the mixture over the outer surface of thermowell for 15 minutes at l,100 1,125 C. and 15 inches Hg. pressure.

4. After titanizing, adjust temperature to tantalum deposition range, l,0l0 1,030 C., and flow C1 at l literj minute through heated tantalum ghips to form TaCl5 and mix the resultant gas with 6.25 liters/ minute of hydrogen passing the mixture over the thermowell surface at 30 torr pressure. All gas flows at STP.

5. Total tantalum deposition time minutes.

6. Turn off chlorine and hydrogen and cool in argon. 7. Deposit thickness from 0.007 inch at underside of hexagon adjacent to threaded coupling, to 0.010 inch 0.020 inch on remaining well surface (0.020 inch at the tip).

It will be noted that the example using stainless steel shows a longer exposure time and a lower temperature than the examples on carbon steel. This is required to avoid eutectic melting by the titanium and nickel in the steel. This melting would occur at normal carbon steel titanizing temperatures.

1 claim: l. A process of depositing a cladding coat on a carbon bearing steel shape which comprises:

a. sand blasting the surface of the shape to remove scale and roughen the surface, b. depositing a coating of iron on said shape by plasma spray, c. placing said shape in a chemical vapor deposition furnace and heating in an atmosphere of argon gas, bubbling hydrogen through-liquid TiCl, and mixing hydrogen with the resultant gas and passing mixture over said shape for approximately 1/2 hour at l,O70 C. to lay down a layer of titanium on said shape, e. adjusting the temperature to a range of 1,010 to 1,0404 C. and flowing chlorine through heated tantalum chips to form TaCl and passing the resultant gas with hydrogen 'gas over said shape for about l/2 hour, increasing the TaCl flow and the hydrogen flow by at least twice the initial flow for a period of about 6 /2 hours, and g. discontinuing the chlorine and hydrogen flow and cooling the shape in argon gas. 2. A process of depositing a cladding coat on a carbon bearing steel shape which comprises:

a. cleaning the shape by degreasing and descaling solutions,

b. placing the shape in a CVD chamber in a vacuum and heating to a range of l,O50 to l,075 C. for 10 minutes,

c. bubbling hydrogen through liquid TiCl mixing the resultant gas with hydrogen and flowing the resultant mixture into said chamberfor 15 minutes at 1,100 to 1,125 C. to lay down a layer of titanium on said shape,

d. subjecting the shape to a mixture of 1aCl obtained by passing chlorine over heated tantalum chips, and hydrogen at a temperature 1,0l0 to l,030 C. for a period of minutes, and

e. discontinuing the chlorine and hydrogen flow and cooling the shape in argon.

3. A process of depositing a cladding coat on stainless steel shape which comprises:

a. cleaning the shape by degreasing and descaling solutions,

b. placing the shape in a CVD chamber in a vacuum and heating to a range of 1,05 0to l,075 C. for 10 minutes, i p

c. bubbling hydrogen through liquid TiCL, and mixing the resultant gas with hydrogen and passing the mixture over the shape at 1,000 C. for about 1 hour to lay on a layer of titanium,

d. adjusting the temperature to 1,0 10C. to l;030 C. and flowing chlorine through heated tantalum chips, mixing the resultant gas with hydrogen and flowing the mixture over said shape for about 5 /2 hours, and

e. discontinuing the flow of chlorine and hydrogen and cooling the shape in argon.

po-wo UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 784,403 Dated Januar 8, 1974 Invehtofls) I FREDERICK A. GLASKI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 5: "pore" should be -pure--,

Column 5, line 27 (Claim 1) "1,0404%" should be 1,o4oc--.

Column 6,, line 12 (Claim 2) I "IaClshould be -Ta'Cl Signed and sealed this 16th da of April 197R.

I (SEAL) j EDWARD MELETQHERQJR; I r 0. I mRSI-IALL DANN Attesting "Officer L Commissioner of Patents 

2. A process of depositing a cladding coat on a carbon bearing steel shape which comprises: a. cleaning the shape by degreasing and descaling solutions, b. placing the shape in a CVD chamber in a vacuum and heating to a range of 1,050* to 1,075* C. for 10 minutes, c. bubbling hydrogen through liquid TiCl4, mixing the resultant gas with hydrogen and flowing the resultant mixture into said chamber for 15 minutes at 1,100* to 1,125* C. to lay down a layer of titanium on said shape, d. subjecting the shape to a mixture of IaCl5, obtained by passing chlorine over heated tantalum chips, and hydrogen at a temperature 1,010* to 1,030* C. for a period of 75 minutes, and e. discontinuing the chlorine and hydrogen flow and cooling the shape in argon.
 3. A process of depositing a cladding coat on stainless steel shape which comprises: a. cleaning the shape by degreasing and descaling solutions, b. placing the shape in a CVD chamber in a vacuum and heating to a range of 1,050* to 1,075* C. for 10 minutes, c. bubbling hydrogen through liquid TiCl4 and mixing the resultant gas with hydrogen and passing the mixture over the shape at 1,000* C. for about 1 hour to lay on a layer of titanium, d. adjusting the temperature to 1,010*C. to 1,030* C. and flowing chlorine through heated tantalum chips, mixing the resultant gas with hydrogen and flowing the mixture over said shape for about 5 1/2 hours, and e. discontinuing the flow of chlorine and hydrogen and cooling the shape in argon. 